Bioreactor performance and quantitative analysis of methanogenic and bacterial community dynamics in microbial...

The use of microbial electrolysis cells (MECs) for H(2) production generally finds H(2) sink by undesirable methanogenesis at mesophilic temperatures. Previously reported approaches failed to effectively inhibit methanogenesis without the addition of nongreen chemical inhibitors. Here, we demonstrated that the CH(4) production and the number of methanogens in single-chamber MECs could be restricted steadily to a negligible level by continuously operating reactors at the relatively low temperature of 15 °C. This resulted in a H(2) yield and production rate comparable to those obtained at 30 °C with less CH(4) production (CH(4)% < 1%). However, this operation at 15 °C should be taken from the initial stage of anodic biofilm formation, when the methanogenic community has not yet been established sufficiently. Maintaining MECs operating at 20 °C was not effective for controlling methanogenesis. The varying degrees of methanogenesis observed in MECs at 30 °C could be completely inhibited at 4 and 9 °C, and the total number of methanogens (mainly hydrogenotrophic methanogens) could be reduced by 68-91% during 32-55 days of operation at the low temperatures. However, methanogens cannot be eliminated completely at these temperatures. After the temperature is returned to 30 °C, the CH(4) production and the number of total methanogens can rapidly rise to the prior levels. Analysis of bacterial communities using 454 pyrosequencing showed that changes in temperature had no a substantial impact on composition of dominant electricity-producing bacteria ( Geobacter ). The results of our study provide more information toward understanding the temperature-dependent control of methanogenesis in MECs.